The Colt Army Special -- a .38-caliber, 5-inch-barrel revolver -- was used by East Chicago, Ind., police Capt. Timothy A. O'Neil to shoot Dillinger, the Chicago Sun-Times reports.
The gun and its holster will be auctioned July 28, days after the 75th anniversary of Dillinger's death, by Leslie Hindman Auctioneers, the auctioneer said.
Because Chicago bans handguns and automatic weapons in the city, an image of the gun, owned by the O'Neil family, will be projected at the auction on a screen, the Sun-Times reported. Potential buyers can see the gun at Shore Galleries in Lincolnwood.
O'Neil, East Chicago police Sgt. Martin Zarkovich and three FBI agents fired shots at Dillinger as he emerged from Chicago's Biograph Theater July 22, 1934.
Word of the auction comes as the new Dillinger movie, "Public Enemies," premieres in Chicago Thursday night. .
Auctioneers predict the gun could fetch much more than their conservative $8,000 to $12,000 estimate, the Sun-Times reported.
Zarkovich's gun sold at auction for $17,550 Nov. 20, 2007, the newspaper said.